Conventional sensing edges generally include a sheath having a cavity formed along the length of the sheath wherein at least a portion of a switch is located. The sensing edge is attached to an edge of a door which may be moved in different directions. When external pressure is applied to the sheath of the sensing edge, the switch is activated. The activated switch actuates a door control device, which in turn causes the door to either stop moving or to open. For example, external pressure may be applied to the sheath when the sheath contacts an obstructing article such as a tool or a portion of the body of a person, located between the sensing edge and an opposed surface. By stopping or changing the direction of movement of the door, damage to the obstructing article may be prevented.
Many types of conventional sensing edges, which operate generally as described above, exist. For example, A first conventional sensing edge includes a photoelectric switch comprising a light transmitter and a light detector. The light transmitter and the light detector are positioned a predetermined distance below a leading edge of a door and at opposite ends of the leading edge such that the light transmitter transmits a light beam across the length of the door toward the light detector. The light beam is blocked from reaching the light detector when an article obstructs the downward movement of the door. When the light detector senses the absence of the light beam, the light detector sends a signal to a door control device, which in turn causes the door to either stop moving or to open.
The first conventional sensing edge is flawed because the light transmitter and the light detector are not contained within a protective covering, such as a sheath. Therefore, the light transmitter and the light detector are subject to damage from natural forces (such as rain, wind, snow, etc.) and artificial forces (such as misdirected balls, errant bicycles, maliciously thrown rocks, etc.).
A second conventional sensing edge includes a mounting member which is attached to the leading edge of a door. The mounting member includes a pair of downwardly extending arms which form a slot-like opening. Extended pockets are located on opposite sides of the arms for receiving the ends of an outer covering. A segment is associated with the outer covering and is located directly beneath and aligned with the slotted opening. A light transmitter and a light detector are located within the slotted opening at opposite ends of the slotted opening such that the light transmitter directs a beam of light across the width of the slotted opening towards the light detector. When external pressure is directly applied to the outer covering, at a precise angle relative to the segment and the slotted opening, the segment is caused to move into the slotted opening, thereby blocking the light beam from reaching the light detector. When the light detector detects the absence of light, the light detector sends a signal to a door control device, which in turn causes the door to either stop moving or to open.
The second conventional sensing edge is flawed because an obstacle is detected only if it causes external pressure to be applied to the outer covering at a precise angle relative to the segment and the slotted opening, such that the segment enters the slotted opening. Obstructions which apply external pressure at different angles relative to the segment and the slotted opening are not detected. Furthermore, the light source and the light detector must be precisely aligned in order to enable the light detector to detect the light beam transmitted by the light transmitter.
A third conventional sensing edge includes a deformable, partially hollow body which is attached to the leading edge of a door. A hollow profile which acts as a light guide is positioned within the partially hollow body, wherein the hollow profile has a slit formed therein. A light transmitter and a light detector are positioned within the hollow profile at opposite ends of the profile such that the light transmitter at one end of the profile transmits a light beam toward the light detector at the other end of the profile. When external pressure is applied to the sensing edge, the profile contained within the partially hollow body is deformed, thereby opening the slit formed in the profile. The opening of the slit allows light to escape (or dissipate) from the profile into the partially hollow body, thereby decreasing the amount of light within the profile and detected by the light detector. If the amount of light detected by the light detector is below a predetermined limit, the light detector sends a signal to a door control device which causes the door to stop moving or to open.
The third conventional sensing edge is flawed because precise alignment and adjustment of the light transmitter and the light detector are necessary due to potential deformations in the profile, particularly deformations in the profile proximate the slit. Such deformations would allow light to escape from the profile into the body, even when external pressure was not applied to the sensing edge. Therefore, the light transmitter and light detector in each sensing edge must be individually precisely aligned and carefully adjusted to compensate for any deformations in the profile proximate the slit. Such alignment and adjustment are necessary even when the interior surfaces of the profile are treated or otherwise coated to be light reflective, since such treatment or coating would not entirely compensate for deformations in the profile proximate the slit.
Therefore, what is required is a sensing edge having a photoelectric switch comprising a light transmitter and a light detector, wherein the light transmitter and light detector are protected from natural and artificial forces, and wherein the switch is activated upon external pressure being applied at any angle to the sensing edge, and wherein precise alignment and adjustment of the light transmitter and the light detector are not required.